1. Field of the Invention
The present invention relates to a jib stretching and folding mechanism of a so-called jib turning type, which turns a jib in stretching and in folding the same, for wheeled cranes, such as truck cranes and rough terrain cranes.
2. Description of the Prior Art
A jib stretching and folding mechanism of a jib turning type disclosed in Japanese Patent Publication No. 63-3827 stores a jib in a storing position along the side surface of a boom, suspends the jib from the storing position, turns the jib through an angle of about 270.degree. about a vertical axis, and then pulls up the jib to stretch the jib from the distal end of the boom, and reverses the stretching procedure to fold the jib.
As is mentioned in Japanese Patent Publication No. 63-3827, the crane of a jib turning type requires human power to turn the jib in stretching and in folding the jib. Accordingly, the large jib of a large crane, in particular, requires hard jib turning work. Furthermore, since such a crane requires manual jib turning work in the middle of jib stretching operation and jib folding operation, it is impossible to carry out jib stretching operation and jib folding operation continuously.